Surfaces having both hydrophobic and oleophobic properties are known as amphiphobic surfaces. The amphiphobic surfaces are characterized by advancing contact angles for water as well as for long chain n-alkanes, such as n-decane, of more than 90° when processed into a flat non-structured surface. Amphiphobic surfaces having high contact angles, for example 120° or higher in the case of water, are very advantageous technically because, for example, they cannot be wetted with water or oil. Dirt particles adhere poorly to these surfaces. The surfaces are highly contamination-resistant because contaminated liquid droplets is slide off the surface and do not evaporate on the surface avoiding stains or spots at the surface.
Various methods for the production of hydrophobic and/or oleophobic surfaces are known in the art. It has been a common practice for improving the water- and oil-repelling properties of a substrate to coat it with a fluorocarbon-based polymer. Other examples of agents which are known to impart hydrophobic and/or oleophobic properties are fluorinated alkylsilanes.
The treatment of a substrate with a single fluorinated alkylsilane is described in, for instance, documents U.S. Pat. No. 6,299,981 B1, EP 0 492 417 A2, EP 0 484 746 A2, EP 0 492 545 A2, and EP 0 525 598 A1.
U.S. Pat. No. 6,340,502 B1 relates to a process for forming a hydrophobic/oleophobic coating on a substrate, preferably glass, by applying a composition containing at least one alkoxysilane and at least one halosilane, each having a perfluorinated group at least one end of their molecule. In the specific embodiment described the coating solution comprises F3C(CF2)7(CH2)2Si(OC2H5)3 and F3C(CF2)7(CH2)2SiCl3 having carbon chains with identical lengths. The water contact angles of the obtained coated substrates are between 105° and 109° which is not very high.
EP 0 477 805 A1 concerns the production of a durable water repellent surface on glass substrates by treatment with a perfluoroalkylalkylene silane in combination with a fluorinated olefin telomer. In the examples a perfluoroalkyl ethylene trichlorosilane composition comprising a range of perfluoroalkyl chains CF3(CF2)n is used, wherein the average n=9.0 and the approximate distribution is C6=6 percent, C8=50 percent, C10=29 percent, C12=11 percent and C14+=4 percent. The distribution of the different perfluoroalkyl groups in the deposited coating is not disclosed. Depending on the substrates on which the perfluoroalkyl ethylene trichlorosilanes in combination with the perfluoroalkyl ethylenes are applied a broad range of water contact angles from 84° to 112° is reported.
EP 0 491 251 A1 relates to a method of forming a monomolecular film of fluorine-containing molecules on a substrate surface. The film comprises at least two different molecules having alkylfluoride groups of different lengths. The two different molecules not only have different molecular lengths, but also belong to different types of compounds selected from the group consisting ofF(CF2)m(CH2)nSi(Rq)(O3-q)  [I]where m represents an integer ranging from 1 to 15, n represents an integer ranging from 0 to 15, the sum of m and n ranges from 10 to 30, q represents an integer ranging from 0 to 2, and R represents an alkyl group or an alkoxyl group, andF(CF2)s(CH2)tA(CH2)pSi(Rq)(O3-q)  [II]where s represents an integer ranging from 1 to 8, t represents an integer ranging from 0 to 2, p represents an integer ranging from 5 to 25, q represents an integer ranging from 0 to 2, A represents a member of a groups consisting of an oxy group, a carbonyl group, a carboxyl-ester group and dimethylsilene group, and R represents an alkyl group or an alkoxyl group. In the embodiment of EP 0 491 251 A1 relating to a singularly adsorbed monomolecular film that is formed directly on a glass surface the two different silanes are used in the coating solution in a mixing ratio of 1:1. Although it is described that the obtained glass surface has sufficient water- and oil-repelling properties, no contact angles are disclosed. Exceptionally high water-wetting angles of from 140° to 150° are only reported for a multilayer coating wherein an additional inner monomolecular film is covalently bonded to the outer monomolecular film comprising the alkyl fluoride groups, said multilayer coating being obtained by a complicated process.
Due to the versatile technical applicability of amphiphobic surfaces there is an ongoing demand for new and efficient methods for preparing those surfaces. It is thus an object of the present invention to provide new types of amphiphobic surfaces and simple methods for preparing those surfaces, preferable by using easily available precursors.